1. Field:
The invention is in the field of flow control and pressure relief valves for controlling the flow of fluid through a pipe line.
2. State of the Art:
Various types of valves are currently in use to control the flow of fluids through a pipe line and to reduce the pressure of a fluid in a pipe line. Where pressure reducing valves are used, it is generally necessary to provide a separate gate valve upstream from the pressure reducing valve and a separate gate valve downstream from the pressuring reducing valve. Further, the pressure reducing valve itself generally has a significantly smaller inlet and outlet diameter than the diameter of the pipe line in which it is installed so that size reducers and other fittings are required to install such valves in the pipe line. When the pressure reducing valves fail, they fail completely, thus allowing flow of fluid through the valve at full pressure which can result in considerable damage to pipes or other items downstream of the valve which are suppose to be protected from such high pressures by the pressure reducing valve.
A common type of pressure reducing valve in use today has a passage that extends from the inlet of the valve, through a valve seat, to the outlet of the valve. A valve disc is positioned against the valve seat to block the flow passage through the valve when it is desired to stop flow of fluid therethrough, and is adjustably positioned a distance from the valve seat to open the passage a selected amount to allow controlled flow through the valve and controlled pressure reduction in the fluid flowing through the valve from inlet to outlet. This type of valve has the disadvantages of relatively large size and weight for a given flow volume and a number of mechanical parts that are subject to wear. Cla-Val Co. of Newport Beach, Calif. manufactures a valve of this type which has four separate valve seats with associated separate valve discs spaced about a valve body.
Rather than using a valve seat and associated valve disc, some valves, such as those manufactured by the Roll Seal Valve Company, Inc. of Temecula, Calif., use an elastomeric liner to control fluid flow. These valves include a valve seat extending circumferentially about the inside of the valve body with the liner extending about an inner portion of the valve body and inflatable so that when filled with a pressurized fluid, will press against the valve seat to close the flow passage through the valve. By controlling the pressure of the fluid in the liner, flow through the valve is controlled. The problem with this type of valve is that the liner can be ruptured or dislodged, thereby causing the valve to fail so pressure is no longer controlled downstream of the valve. Another problem is that if the liner ruptures or becomes dislodged, the valve must be removed in order to replace the liner.